This invention relates in general to print wheels and more particularly to a method of assembling a print wheel comprised of a plurality of individual piece parts.
Printing elements for serial printers shaped generally in the form of a wheel or the like have been known for some time. By way of example, see U.S. Pat. Nos. 2,236,663, 3,461,235, 3,498,439, 3,651,916, 3,859,712 and 3,884,340.
If the print wheel is to be used in a high-speed serial printer requiring rapid bidirectional rotation, it is preferred that the print wheel be light in weight. It is also preferred that the beams or arms of the print wheel be flexible.
Diablo Corporation, a subsidiary of the present assignee, has marketed a serial printer under the trade name Diablo Hytype I, which has a print wheel having a plurality of character slugs located at the ends of spokes or beams extending radially outwardly from a control hub. The print wheel is rotated by a servo mechanism to position selected characters opposite a print hammer and ribbon at a printing station location. The Hytype I printer has enjoyed commercial success as an electronic serial printer capable of high speed and versatile operation. The print wheel, which the Hytype I printer employs, is basically a single element structure in that the central hub, beams and slugs are an integrally molded thermoplastic structure fabricated in accordance with injection molding techniques. This print wheel gives excellent performance with very favorable economics, i.e., the integral wheel is relatively inexpensive to manufacture. Nonetheless, when subjective standards of print quality are encountered in certain applications, the integral structure print wheel does not always give the desired print quality.
Specifically, in automatic text-editing typewriter or office-typing environment, the demands upon a print wheel are great; the demands for high print quality cause the print wheel to be subjected to about ten times greater force because of about five times greater hammer energy compared to a Hytype I printer operating as a computer output terminal, for example. The present assignee is marketing an automatic text-editing typing system for application in the office environment under the trade name of Xerox 800 Electronic Typing System, which employs the printing mechanism of the Diablo Hytype I but with the inclusion of various modifications. One of the modifications made to upgrade the print quality was the provision of a composite-type print wheel, such as that disclosed in U.S. patent application, Ser. No. 509,193, filed Sept. 25, 1974, in the name of Gordon Sohl et al., titled "Composite Print Wheel", the disclosure of which is incorporated by reference into this specification.
A plastic, integral print wheel performs satisfactorily in both the high speed and energy modes mentioned above but not with the same print or image quality over the same life span. Loss in image quality is generally judged as the first fall off in image resolution detectable by the unaided eye. The composite wheel, on the other hand, performs excellently over a very broad range of operating conditions.
While the plastic, single element print wheel is fabricated as an integral molded thermoplastic structure using injection molding techniques, the plurality of individual piece parts of the composite print wheel must be assembled together as a functional unit. The individual piece parts must be assembled with a relatively great degree of accuracy in order to maintain the horizontal and vertical registration alignment of the various print characters, located on the plurality of character slugs, with respect to the center about which the print wheel rotates. The conventional manner of controlling the tolerances of the mating individual parts did not result in an assembled print wheel, which would meet the required specification and tolerance, relative to vertical and horizontal placement or location of the print characters with respect to the center of the hub, of print quality required in the office typing environment.
Accordingly, it is a primary object of the present invention to provide an improved method of assembling a print wheel comprised of a plurality of individual piece parts.
Another object of this invention is to provide an economical and effective method of assembling a print wheel comprised of a plurality of individual piece parts.
A further object of the present invention is to provide a novel method of assembling a print wheel comprised of a plurality of individual piece parts.
Other objects and advantages of the present invention will be evident from the specification and claims when read in conjunction with the accompanying drawing illustrative of the invention.